Russian President Vladimir Putin makes his New Year Address to the nation ahead of 2017 in the Kremlin, Moscow, Russia, on Dec. 31, 2016.

Russian President Vladimir Putin makes his New Year Address to the nation ahead of 2017 in the Kremlin, Moscow, Russia, on Dec. 31, 2016.

(Mikhail Klimentyev, Sputnik/Kremlim/EPA)

Greg MillerThe Washington Post

Russia carried out a comprehensive cyber campaign to sabotage the U.S. presidential election, an operation that was ordered by Russian President Vladimir Putin and ultimately sought to help elect Donald Trump, U.S. intelligence agencies concluded in a remarkably blunt assessment released Friday.

The report depicts Russian interference as unprecedented in scale, saying that Moscow's role represented "a significant escalation in directness, level of activity, and scope of effort" beyond previous election-related espionage.

The campaign initially sought to undermine public faith in the U.S. democratic process, "denigrate" Democratic presidential candidate Hillary Clinton and damage her expected presidency. But in time, Russia "developed a clear preference for President-elect Trump" and repeatedly sought to artificially boost his election chances.

The report released to the public is an abbreviated version of a highly classified multiagency assessment requested by President Barack Obama. Even so, it amounts to an extraordinary postmortem of a Russian assault on a pillar of American democracy.

The 14-page document made public also serves as an explicit rebuttal to Trump's repeated assertions that U.S. spy agencies cannot determine who was responsible for a hacking operation that extracted thousands of emails from Democratic Party computer networks and dumped them into public view via the WikiLeaks website.

In the report, the CIA, FBI and Office of the Director of National Intelligence concluded with "high confidence" that Russian intelligence services penetrated numerous computer systems tied to U.S. political parties and then "relayed" the email troves to WikiLeaks.

Trump emerged from a briefing by the nation's top intelligence officials on the contents of the report acknowledging at least the possibility that Russia was behind election-related hacks. But he offered no indication that he was prepared to accept their conclusions that Moscow sought to help him win.

Instead, Trump said in a statement that while Russia, China and other countries and groups may have sought to breach Democratic and Republican computer systems, "there was absolutely no effect on the outcome of the election."

The report did not address that issue. It was presented to Trump by officials including Director of National Intelligence James Clapper Jr., CIA Director John Brennan and FBI Director James Comey.

Trump also said that "there was no tampering whatsoever with voting machines." That appeared to be consistent with the findings of the report, although it noted that Russia "obtained and maintained access" to numerous election systems that "were not involved in vote tallying."

A footnote on the document said that the conclusions contained in the declassified draft were "identical to those in the highly classified assessment but this version does not include the full supporting information on key elements of the influence campaign."

Obama commissioned the report shortly after the Nov. 8 election, and recently ordered a series of retaliatory measures including new economic sanctions, the expulsion of dozens of suspected Russian intelligence operatives from the United States and the closure of two Russian-owned compounds in the country.

The report was met with mixed reactions from senior lawmakers. Sen. Richard Burr, R-N.C., the chairman of the Senate Intelligence Committee, described the Russian activities cited in the report as "a troubling chapter in an ongoing story, and I expect that our nation's leaders will counter these activities appropriately."

His counterpart in the House, Rep. Devin Nunes, R-Calif., used the report to criticize Obama, saying that the House Intelligence Committee "has been warning the Obama administration for years about the need for stronger measures against Russia . . . but our warnings largely fell on deaf ears."

The public version of the report does not explicitly mention some of the most sensitive pieces of intelligence that helped analysts reach their conclusions. U.S. officials have said that spy agencies identified certain "actors" involved in the cyber offensive, believe Russia was far more focused on penetrating and exploiting Democratic systems, and intercepted communications making clear that top Russian officials congratulated themselves on Trump's win.

Then-National Intelligence Director James Clapper and Cyber Command Chief Admiral Mike Rogers were among the intelligence community officials called to testify before the Senate Armed Services Committee on Russia's hacking leading up to the 2016 presidential election as well as cyber threats facing the United States. Jan. 5, 2017.

Then-National Intelligence Director James Clapper and Cyber Command Chief Admiral Mike Rogers were among the intelligence community officials called to testify before the Senate Armed Services Committee on Russia's hacking leading up to the 2016 presidential election as well as cyber threats facing the United States. Jan. 5, 2017.

One of the report's key judgments is that "Putin and the Russian government aspired to help President-elect Trump's election chances when possible by discrediting Secretary Clinton and publicly contrasting her unfavorably to him."

Moscow did so in part because it "developed a clear preference for President-elect Trump," who as a candidate repeatedly praised Putin and advocated policies in Syria and Europe strongly favored by the Kremlin.

But the report also attributed Russia's efforts to Putin's hostility toward Clinton, a former senator and secretary of state whom he blamed for inciting mass protests against his government in 2011 and 2012.

Overall, the report describes a multipronged campaign that involved not only hacking, but overt propaganda on Russian-controlled news platforms and the extensive use of social media and even "trolls" to amplify voter discord in the United States and encourage opposition to Clinton.

Despite those exertions, Russia appears to have concluded that a Clinton victory was inevitable right up until election night. As a result, Moscow focused on finding ways to undercut Clinton's legitimacy if she won.

One of the more colorful notes in the report describes how "pro-Kremlin bloggers had prepared a Twitter campaign, #DemocracyRIP, on election night," then had to shelve it when Trump won.

The document traces interference efforts that began with inconspicuous probes of U.S. electoral systems in early 2014, carried through the election, and may still be underway.

Russian intelligence agencies first gained access to Democratic National Committee networks in July 2015, the report says. Russia's miliary intelligence service, known as the GRU, "probably" expanded its efforts in March 2016, going after the email accounts of Democratic Party officials and other political figures.

By May, the GRU had stolen what the report describes as "large volumes of data from the DNC." In the ensuing months, chunks of that trove began to appear on websites including WikiLeaks, generating a steady stream of headlines that embarrassed Democrats and kept voter attention on Clinton's email controversy.

Putin has repeatedly denied that Russia was responsible for the hacked emails. In an interview with the New York Times on Friday, Trump called the sustained focus on the issue a "political witch hunt."

The intelligence assessment also drew the most direct line to date between Putin's desire to aid Trump's campaign and Russia's policies and objectives in Syria and Ukraine. In both cases, it said, Putin "indicated a preference for President-elect Trump's stated policy to work with Russia, and pro-Kremlin figures spoke highly about what they saw as his Russia-friendly positions" in those two countries.

Putin is also eager for relief from economic sanctions imposed on Russia for its support of separatist forces in Ukraine and its annexation of Crimea.

As recently as this week, Trump appeared to be siding with WikiLeaks founder Julian Assange - who has denied that his website got purloined emails from Russia - over the determinations of the CIA and FBI.

The report provides new details about U.S. intelligence agencies' view of WikiLeaks and its relationship with Russia. "We assess with high confidence that the GRU relayed material it acquired from the DNC and senior Democratic officials to WikiLeaks," the report said. "Moscow most likely chose WikiLeaks because of its self-proclaimed reputation for authenticity."

The report noted that none of the files passed to WikiLeaks contained "evident forgeries."

The document said that "Guccifer 2.0," the online identity of a hacker purportedly involved in the campaign, "made multiple contradictory statements and false claims about his likely Russian identity throughout the election." It was the document's clearest indication that U.S. spy agencies believe they have identified him.

In some ways, Russia's intervention in the 2016 election is consistent with a long-standing pattern that traces back to the Soviet Union of espionage against prominent politicians and policymakers in the United States. U.S. spy agencies also devote significant resources to gathering intelligence on Putin and his subordinates.

The report suggests that beyond his animosity toward Clinton, Putin may also have been driven by his own conviction that Moscow has been repeatedly targeted with embarrassing leaks that he attributes to the United States, including the Panama Papers files that showed how wealthy individuals close to the Kremlin had hidden their fortunes, as well as material that helped expose the doping scandal among Russia's Olympic athletes.

Putin's success in using cyber capabilities and propaganda to disrupt a U.S. presidential race is likely to embolden him to mount similar operations against the United States and its allies in the future. "We assess Russian intelligence services will continue to develop capabilities to provide Putin with options to use against the United States," the report said.

The Washington Post's Karen DeYoung and Julie Tate contributed to this report.